This invention relates to a method for treating paper filters contaminated by oil, rust particles and other undesirable contaminants. In a more particular aspect, this invention concerns itself with a method for recovering halogenated vacuum pump oils, such as chlorotrifluoroethylene, from contaminated paper filters which are used in oil purification processes.
At the present time, a number of oil purification processes utilize a vacuum technique to affect purification of oils. Generally, the vacuum pump used to create the necessary vacuum uses a halogenated vacuum pump oil which flows through a series of paper filters. After a period of time, the paper filters become clogged with contaminants from the pump oil and are no longer effective.
As a result, the filters were disposed of even though they contained substantial amounts of oil trapped by the filters' fibers. Disposing of the paper filters, however, constituted a wasteful and expensive practice since large amounts of the vacuum pump oil were discarded along with the filters.
It became extremely important, therefore, that a system be developed that would eliminate the waste involved in discarding paper filters and provide a means for lowering the costs involved in oil purification procedures. The need for such a system that is safe, reliable, inexpensive and ecologically acceptable becomes of paramount importance when one considers the considerable cost involved in using vacuum pump halocarbon oils which are relatively expensive. As a result of this need, a considerable research effort was undertaken in an attempt to overcome this problem and provide a means for recovering the vacuum pump oil in a non-contaminated condition for subsequent reuse in a vacuum pump.
As a result of that research effort, it was found that the problem of removing vacuum pump oil from paper filters, along with the simultaneous problem of eliminating contaminants from the vacuum pump oil itself, could be accomplished by first submerging the oil-saturated paper filters into an extraction bath containing a mixture of trichlorotrifluoroethane and water followed by vacuum distilling the extractive to recover the halocarbon pump oil in reasonably pure and uncontaminated form.